The present disclosure relates to a battery charger.
A battery charger is known which is configured such that a battery pack with a battery stored therein is attachable and detachable so as to charge the battery when the battery pack is attached.
This type of battery chargers and battery packs are each provided with a positive electrode terminal and a negative electrode terminal for allowing the passage of charging current. When the battery pack is attached to the battery charger, a positive electrode terminal of the battery charger and a positive electrode terminal of the battery pack are electrically coupled while the negative electrode terminal of the charger and the negative electrode terminal of the battery pack are electrically coupled. This state allows supply of charging current from a charging power supply circuit of the charger to batteries.
Some of known battery chargers are each provided with a signal input terminal disposed separately from the terminals for charging current in order to obtain from a battery pack an analog signal indicating various information related to the inside of the battery pack (including the temperature and the voltage of battery cells).
When a battery pack having a signal output terminal that outputs the analog signal indicating the various information is attached to the battery charger, the signal input terminal of the battery charger and the signal output terminal of the battery pack are electrically coupled. Through these terminals, the analog signal is inputted from the battery pack to the battery charger.
A signal processor of a battery charger for processing an analog signal (for example, a microcomputer) obtains various information based on the analog signal inputted from the battery pack. The signal processor also monitors the state of a battery and controls charging of the battery based on the obtained information.
For example, in a case where the battery pack is provided with a thermistor for detecting the temperature of a battery and configured such that the voltage of the thermistor indicating the temperature of the battery is outputted in the form of an analog signal from the signal output terminal, the signal processor of the battery charger is capable of detecting the temperature of the battery based on the analog signal (i.e., the voltage of the thermistor) inputted from the battery pack through the signal input terminal. Subsequently, the signal processor, for example, compares the detected temperature with a threshold. If the detected temperature exceeds the threshold, it is determined that the temperature of the battery is high, and the signal processor performs a predetermined process (for example, forcible stop of charging).
The signal processor described above detects an electrical potential (voltage value) of the analog signal with respect to the reference potential (to be also referred to as “ground”) set in the battery charger. The ground may be set at any suitable point. The ground may be set, for example, at the negative electrode terminal (that is, the negative electrode of the charging power supply circuit) as in a first example disclosed in the publication of Japanese Patent No. 3375822. Alternatively, for example, a ground and a ground terminal for the analog signal may be disposed separately from the negative electrode terminal so as to provide an independent transmission path for the analog signal separately from the transmission path for charging current as in a second example disclosed in the Unexamined Japanese Patent Application Publication No. 2001-211559.